testing bias/lightbulb limiter

[jeff]

 Can you test/set bias on your amp when it's plugged into your lightbulb limiter? I saw a video where someone suggested to do this.
Aren't you gonna get a different bias from when you use the amp plugged directly into the wall?
 Inotherwords with the lightbulb in series isn't there going to be a voltage drop and not give you the correct bias when you run the amp normally?
Thanks
Jeff

[eleventeen]

I wouldn't do that. The lightbulb limiter is a device you use primarily to detect and prevent damage from some catastrophic fault. Either a build error, or an unknown amp you have never seen plugged in, or a customer repair where you don't know about the customer's ability to explain any fault. Or if the amp smells like burnt electrical, that's when you plug it into the LL.


You build an amp, check your work, but maybe you made some crazy mistake or dropped a piece of wire or solder blob where it is shorting something but you can't see it. You plug into the LL so that if there is some massive short it doesn't blow stuff up or start a fire the first, second, third time you plug it in. Then you should be pretty much done with it.


*IF* you built an amp with variable bias and you have never powered it up, my own practice and opinion is that you should crank the bias as cold as you can (maximum negative voltage) for first turn-on. The output tubes should be as shut off as you can make them. Of course, you can measure that bias with no output tubes installed. Say the schematic calls for -35 volts. I like to have -50 or -60 on there to start. Plug into your LL. Turn it on, see that the little tubes light up. Turn off. Install the power tubes, do it again, see the fils light up, be sure no smoke. Maybe go check 6-8-10 plate voltages. If everything is good, delete the LL and launch the thing. 

Another thing I usually do when servicing an amp is to solder a teeny thin wire across the fusepost and remove the fuse. The wire is a single strand from a scrap of stranded wire. Fuses are like 75 cents each now, no need to blow up three or four of them if you have something goofy going on. Oh yeah....snip the little wire and replace the fuse when you're done!

An amp you've never seen before that you bought at a garage sale and maybe hasn't been plugged in for 20 years, yeah, you start it out on the LL. Or a variac.

Once you have confirmed you have no disaster going on, you're done with the LL.

[stratele52]

Can you test/set bias on your amp when it's plugged into your lightbulb limiter? I saw a video where someone suggested to do this.
 
Jeff

No ,


Bulb light is a current limiter . You don't have full voltages on your amp . You can't set you bias properly


Any link for this video ? .